Competing charge density wave phases in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>YNiC</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>

Charge density wave (CDW) orders in <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msub><a:mi>YNiC</a:mi><a:mn>2</a:mn></a:msub></a:math> are studied by means of combined experimental and computational techniques. On the experimental side, single crystals grown by the floating-zone method were examined by means of x-ray diffraction, as well as transport and thermal techniques. Density functional theory (DFT) calculations founded on the experimentally determined parent and CDW-modified crystal structures provide details of electronic and phononic structures as well as electron-phonon coupling and resolve changes inflicted upon entering the different CDW phases. Thereby, contrasting effects of subsequently emerging CDW states characterized by incommensurate <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:msub><b:mi>q</b:mi><b:mrow><b:mn>1</b:mn><b:mtext>ic</b:mtext></b:mrow></b:msub></b:math> and commensurate <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:msub><c:mi>q</c:mi><c:mrow><c:mn>2</c:mn><c:mtext>c</c:mtext></c:mrow></c:msub></c:math> modulation vectors are revealed. The former state, on-setting below <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mrow><d:msub><d:mi>T</d:mi><d:mtext>1ic</d:mtext></d:msub><d:mo>≃</d:mo><d:mn>305</d:mn><d:mspace width="0.16em"/><d:mi mathvariant="normal">K</d:mi></d:mrow></d:math>, weakly modifies the electronic structure by opening an almost isotropic gap on a minor part of the Fermi surface (FS). The latter phase, which takes over below <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:mrow><g:msub><g:mi>T</g:mi><g:mtext>2c</g:mtext></g:msub><g:mo>≃</g:mo><g:mn>272</g:mn><g:mspace width="0.16em"/><g:mi mathvariant="normal">K</g:mi></g:mrow></g:math> has a more pronounced impact on physical properties via a decomposition of larger parts of the FS. These dissimilar behaviors are directly reflected in the electronic transport anisotropy, which is significantly weakened in the <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"><j:msub><j:mi>q</j:mi><j:mrow><j:mn>2</j:mn><j:mtext>c</j:mtext></j:mrow></j:msub></j:math>-type CDW state. As revealed by our DFT studies, CDW phases are very close in energy and their origin is directly related to the anisotropy of electron-phonon coupling, which is linked to a specific orbital character of related FS sheets. Specific heat and thermal expansion studies reveal a nearly reversible first-order phase transition at around <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"><k:mrow><k:msub><k:mi>T</k:mi><k:mtext>2c</k:mtext></k:msub><k:mo>≃</k:mo><k:mn>272</k:mn><k:mspace width="0.16em"/><k:mi mathvariant="normal">K</k:mi></k:mrow></k:math>, where both CDW phases coexist within a <n:math xmlns:n="http://www.w3.org/1998/Math/MathML"><n:mi>T</n:mi></n:math> interval of about 10 K.